Analysis and simulation of a new algorithm for spotlight-mode synthetic aperture radar

An algorithm was proposed for computer-aided tomography and spotlight-mode synthetic aperture radar in a recent work by W. Lawton (IEEE Trans. Acoust., Speech, and Signal Process, vol.36, p.933-971, June 1988). This processing scheme assumes that Fourier transform samples of the projections obtained lie on a concentric-squares polar grid. The spatial-domain image is produced through a series of convolutions and DFTs (discrete Fourier transforms), all performed using FFTs (fast Fourier transforms). The algorithm requires O(N²logN) operations to produce an N ×N image and is made possible by the geometry of the concentric-squares polar grid. The present authors more completely describe the Lawton algorithm and derive a closed-form, approximate expression for its impulse response for the case of spotlight-mode synthetic aperture radar. A formula is given for the exact number of multiplications required by the algorithm, and a set of simulated point target responses is given to help assess the image quality provided by the algorithm